Sensory organs


Sensory organs are very highly developed and specialized organs that are an extension of the central nervous system, with a sole function to take in information and relate it to the brain. The sensory neurons are highly adapted to detect changes of both external and internal changes in the environment and report these changes to the brain. Whether through touch, sound, taste, sight, or smell, the senses are constantly reporting variances, nuances, and dramatic changes within the environment to the brain. This is done through nerve actions, or action potentials.

A stimulus, through any nerve pattern, is sensed and must be interpreted by the brain in an uninterrupted flow in order for the sense to become real for the body. The sensory system supplies the body with pleasurable sensation as well as warning the body to dangers, such as the sensation of heat, the sounds which warn, and the smell of toxic chemicals, smoke, or other alerting odors. This combination of stimuli makes the sensory system on of the most complex in the human body.


The brain’s interpretations of the sensations determined by the sensory system are called perception. Perception is the brain’s method of determining whether the information sent to the brain is pleasurable, painful, dangerous, or joyful. These perceptions explain to the body how to respond to the stimuli. Without this communication, the sensory system is useless.

Perception applies to internal stimuli as well. Perception tells the body of hunger, thirst, itching, or other bodily needs. This state of perception keeps the body alive. Without the perception of thirst, the body would dehydrate. Without the perception of hunger, the body would starve.

The perception of sensation requires stimulus that is strong enough for the information to be sent to the brain and interpreted. It also requires a receptor, which converts the stimulus from simple and basic stimulus into a nerve pulse in order for the brain to receive the information. A receptor is located at the end of a sensory nerve fiber and is a highly specialized peripheral dendritic which operates the nerve cells. Finally, it requires the nerve impulse to travel to the brain and the brain’s ability to interpret the information.

The cerebral cortex is the part of the brain responsible for the interpretation of impulses and responds to the transmission of information sent via nerve impulses and creates the necessary perception. If the nerve impulses do not reach the cerebral cortex, the brain is not able to interpret the information transmitted and the stimulus remains uninterpreted. Impulses that may be interrupted and lost in the brain stem or the central spinal cord may create an unconscious reflex or unintentional motor response but do not create awareness or decisive action from the brain.

Ascending tracts are created when the stimulus which requires interpretation via the nerve pulse’s transmission only when they reach the cerebral cortex. Nuclei, which are tiny groups of neuron cells, produce synaptic sites along the central nervous system. The central nervous system houses these synaptic sites along the sensory tracts. In its simplest explanation, it is much like a series of railroad tracks with stations along the way. The information must be passed from station to station in order to reach the final destination, the cerebral cortex. The most vital “stations” that the sensory information must pass through on its way to the central cortex include the medulla oblongata, pons, and thalamus, which are conveniently located in the spinal cord.


Scientific studies have allowed for great understanding of the transmission of information between the basic senses and the brain. Perception is in fact condensed into a very narrow range. The senses act as filters, and this narrow range of sensory capabilities are a safety net of sorts to prevent the brain from becoming overloaded with sensory information while simultaneously allowing the brain to form perceptions about information necessary for basic survival but nothing beyond that. For instance, vision is restricted to the transmission of information gathered via the light rays in the visible vision spectrum. This allows for keen and sharp site without overloading the vision sensory passageways. X-rays, ultraviolet lights, and infrared lights can not be seen with the naked human eye. There is no acute survival need for these ranges of vision and thus they were denied to the human eye.


The complex design of the receptors and the neural pathways are considered to be either general or special, depending entirely on their function and the degree of technique associated with its use. The location of the receptors determines whether they are classified as visceral or somatic. The structural design of the sensory receptors may either encapsulated within non-neural structures such as the preceptors which allow the skin the feel pressure, or they may be free such as the receptors which transmit the feeling of pain or temperature or sensations such as smooth, rough, or prickly. Photoreceptors in the eyes, taste buds on the tongue, and the hair cells of the inner ear are excellent examples of receptors that were formed from epithelial cells that synapse with sensory dendrites.
Sensory organs
Image: Sensory Organs

While the five senses are considered the basic starting block for the sensory system, each sense has additional senses that work within its framework, creating a multitude of senses. The sense of touch has pain, cold, heat, and so forth within its framework of additional senses. The senses are considered either general if their pathways of communication are basic and simple and are considered special if the pathway of communication are complex or require distortion by the sensory system.


General senses, such as those of touch and simple elemental basics of touch like temperature, are common throughout the body’s entire sensory system. Specialized and highly developed senses are scattered in the complex receptor organs and their pathways to the brain (the railroad tracks with stations) are remarkably complex and high developed. These specialized senses include sight, balance, taste, and smell. Depending on their location, each sense is separately classified as visceral or somatic.

Visceral senses are encased within the visceral organs. Visceral organs pertain to organs which are internally located, particularly of the torso or abdomen, such as the lungs, heart, liver, spleen, and so forth. Somatic sensory receptors are those which are located within the body wall, such as the sense of touch with receptors located on the skin.

Visceral senses and somatic sense can be used in some cases interchangeably. The sense of hearing, for example, or pain within a visceral organ. The pain is a general sense which is typically considered to be general and somatic, however, pain within a visceral organ refers to a general sense that is now in a visceral location.

The receptors are separated into three basic types, classified in three categories such as exteroceptors, visceroceptors, and proprioceptors. Exteroceptors are responsible for responding to stimuli that is located on the surface of the body; external stimuli. The receptors on the skin, the rod and cone cells of the retina (photoreceptors), chemoreceptors (receptors responsible for the sensation of smell), and mechanoreceptors which are hair follicle receptors located within the middle ear to detect the sense of sound.

The receptors in the dermis have numerous additional receptors, one for each basic sensation. Thermorectpors indicate information that can be translated into temperature. Mechanoreceptors indicate the appropriate information to interpret pressure. Tactile receptors transmit information to interpret touch sensations such as soft or rough. Nociceptors transmit the information needed to interpret pain. Pain is determined through the release of chemicals that communicate with the nociceptors. Any receptor can transmit the information necessary to indicate pain is over stimulated.

Viceroceptors indicate sensation located internally. This can include hunger, thirst, and internal pain. Chemoreceptors are internal receptors that are responsible for indicating changes in the body’s levels of gasses, a body low on oxygen will feel faint or lightheaded when the chemoreceptors indicate there is not ample oxygen in the system. Changes in the blood pressure are indicated by receptors known as baroreceptors.

Proprioceptors indicate information necessary for the brain to understand the body’s position. Located between tendons and muscles, the inner ear, and in and around joints, the proprioceptors indicate the information for interpretation of movement, balance, and position.

Sensory receptors are also classified as determined by their ability to adapt to stimuli. All receptors that are introduced to a new sensation fire quickly with a great burst of enthusiasm, but some will accommodate (or get used to) the new stimuli. Some receptors will continue to fire with the same amount of enthusiasm regardless of the length or duration of the stimuli. Phasic receptors are those which indicate new stimuli with great enthusiasm and then accommodate over time. Receptors which maintain their rate of enthusiasm throughout the entire duration of the stimuli are known as tonic receptors.

The sensory system is a very complex and notable intricate system that the body can not survive without. While the loss of one or even two basic senses can be readily adapted to, the loss of the entire sensory system would render a body incapable of survival in the world.
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human anatomy Organs included in Sensory organs

Bulbs of krauseCavities and chambers of the eyeballCochlea
ConjunctivaCorpuscle of touchExtrinsic ocular muscles
EyeballEyelids and eyelashesFree nerve endings
Gustatory senseInner earInternal tunic
Lacrimal apparatusLamellated corpusclesMiddle ear
Olfactory senseOrbit and eyebrowsOrgans of ruffini
Outer earProprioceptorsSemicircular canals
Sense of hearing and balanceSomatic sensesThermoceptors
Vascular tunicVestibuleVisual sense